This description relates to the structure of a rail road car underframe, and, in particular, to the assembly of that underframe. Many railroad cars have what are commonly referred to as straight through center sills, as distinguished from stub sills. A straight through center sill runs the full length of the body unit of the car. Often simply the term “center sill” is used when discussing a car with a full center sill.
One type of car that has been known for some years is what is commonly referred to as a bathtub gondola car. In a traditional gondola car the floor or deck of the gondola is a substantially flat sheet (or assembly of sheets) that is carried at roughly the level of the top flange of the center sill, above a set of cross-bearers and cross ties. In a bathtub car, the floor of the gondola is not flat, but rather bulges downwardly between the sidebeams. To some people, the downwardly bulging lading containment skin bears a resemblance to a bath tub. In one particular type of bathtub gondola car, there are two parallel “tubs”, each of the two tubs being mounted between the center sill and a respective one of the side sills of the side beams of the car. An example of such a double tub gondola is shown in U.S. Pat. No. 4,361,097 of Jones, issued Nov. 30, 1982. In this car, the center sill functions both to provide a vertical load path for the tubs and to provide a longitudinal path for buff and draft loads. In the first role, it may be noted that coal car tubs (and other fittings) are sometimes made of materials other than steel. For example, the tubs and portions of the sidewalls may be made of aluminum. Some of the sidewall sheets may be made of stainless steel.